Knock control process for an internal combustion engine

ABSTRACT

A process for adaptive knock control for an internal combustion engine serves to retard the firing angle of an internal combustion engine when knocking occurs and then to advance the firing angle again. At the same time, the operation of the internal combustion engine is subdivided into various operating ranges; on leaving an operating range, a value is always saved as a retardation of the firing angle determined during operation in this range, and when starting up again in this range with load dynamics and/or speed dynamics also occurring at the same time, this saved value is output as the starting value for operation in this new operating range.

BACKGROUND INFORMATION

A knock control process is described in German Patent No. 40 08 170,where the firing angle is adjusted by using an engine characteristicsmap based on the operating parameters detected, and when knockingoccurs, the firing angle is retarded to prevent knocking. Then theretarded firing angle is adjusted back to the mapped firing angle byadvancing it incrementally. With this known knock control method, theoperating range of an internal combustion engine is subdivided intovarious ranges. On leaving an operating range during operation of theinternal combustion engine, the instantaneous firing angle is saved, andwhen the internal combustion engine is operated in this range again, thesaved firing angle is output as the starting value.

SUMMARY OF THE INVENTION

The process according to the present invention has the advantage, incomparison with the known process, that it prevents sudden changes infiring angle. Therefore, there are no sudden changes in engine torqueeither, so driving comfort is improved.

It is advantageous to retain the firing angle from the precedingoperating range that was the prevailing firing angle when leaving thisoperating range for operation in the new operating range if the loadand/or speed dynamics when changing ranges do not exceed a predefinedvalue; the value that can be predefined is determined for the variousoperating conditions in the application and is saved in a memory. Inaddition, it is advantageous to calculate a representative value for thefiring angles that have occurred in the previous operation of theinternal combustion engine in this range and to use this value as thestarting value for the firing angle for operation of the internalcombustion engine after changing ranges. Ultimately, the enginecharacteristics map in the microprocessor can be continuously updated onthe basis of operating parameters for output of the firing angle so theknock limit is constantly being learned by the microprocessor. This canbe accomplished, for example, by having the last firing angle beforeoccurrence of knocking entered in the engine characteristics map as thenew firing angle for this operating point. Another possibility is forthe first firing angle after knocking occurs to be entered in the enginecharacteristics map. It is also conceivable to apply a small correctionsuch as a definable firing angle displacement ΔZW to the firing anglebefore knocking occurs and then enter this value in the enginecharacteristics map. Moreover, it is also possible for this correctionof the mapped firing angle to be implemented only if the firing anglesaved in the engine characteristics map differs from the new firingangle to be entered in the engine characteristics map by a predetermineddifference DZW. This has the advantage that it ensures operation of theinternal combustion engine as close to the knock limit as possible.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 show a schematic diagram for an adaptive knock control process.

FIG. 2 an adaptive engine characteristics map.

FIG. 3 illustrates the change in the firing angle on the basis of theprocess according to the present invention, and

FIG. 4 show a diagram of the individual process steps.

DETAILED DESCRIPTION

FIG. 1 shows a block schematic for carrying out the process of adaptiveknock control. The internal combustion engine (not shown) is operatedwith a controller 1 that has a knock sensor analysis circuit 2, amicroprocessor 3, an analog-digital converter 4 and a firing outputstage 5. One or more knock sensors 6 are provided on the engine block ofthe internal combustion engine and are connected to the knock sensoranalysis circuit 2. Knock sensor analysis circuit 2 is connected tomicroprocessor 3 via analog-digital converter 4. The measured parametersof the internal combustion engine are also sent to microprocessor 3.Thus, for example, the load L, which is determined from the throttlevalve angle setting and/or the intake manifold pressure, the speed n andtemperature T are sent to the microprocessor. Signal KS representing theengine noise is detected by the knock sensor and sent to knock sensoranalysis circuit 2. By comparison with a reference value, this analysiscircuit 2 determines whether knocking K has occurred. When knockingoccurs, the firing angle output by the microprocessor on the basis ofthe engine characteristics map is retarded and then subsequently thefiring angle is advanced again, which corresponds to approximating it tothe firing angle output from the engine characteristics map. This knockcontrol with the required firing angle adjustment is performed bymicroprocessor 3. On the basis of the available operating parameters,microprocessor 3 calculates a mapped firing angle to which an adaptivefiring angle adjustment Δα is applied after knocking occurs. An adaptiveengine characteristics map like that illustrated in FIG. 2 is stored inmicroprocessor 3. This adaptive engine characteristics map is subdividedinto individual operating ranges as a function of load L and speed n.German Patent No. 40 08 170 for example contains a detailed descriptionof this adaptive engine characteristics map.

The knock control process according to the present invention will now beexplained with reference to FIG. 3, which illustrates the operation ofthe internal combustion engine in any observation period. At time t0 acombustion engine begins to operate in operating range I. The controllerdetermines a firing angle α_(KF) on the basis of the current measuredoperating parameters using an engine characteristics map generated fromspeed and load. Knocking K is detected during operation of the internalcombustion engine in operating range I. Then the firing angle isretarded by Δα. The extent of retardation of the firing angle depends onthe knocking intensity. Then the firing angle is returned by advancingit incrementally, thus approaching the mapped firing angle. Thisrestoration of the firing angle is continued until knocking K occursagain or until reaching the mapped firing angle. In the embodimentaccording to FIG. 3, knocking K occurs once more during operation inoperating range I, so the firing angle is again retarded. At time t1 theinternal combustion engine changes operating ranges, e.g., from loadoperation to deceleration operation. On leaving operating range I, thelast firing angle α_(ZWI) for this operating range is saved in a memoryof microprocessor 3. It is also conceivable to save a firing anglecalculated from all firing angles in this operating range, e.g., theaverage value, instead of saving the last firing angle.

At time t1 there is a change of operating range, i.e., leaving the rangeof the adaptive engine characteristics map and entering a new range. Inthe present case in FIG. 3, there is a change from range I to range II.This first occurrence of range II in the observation period in questionin FIG. 3 is designated as IIa, to illustrate the fact that this rangeII occurs for the first time in the observation period illustrated here.The firing angle output at time t1 illustrates the conventional firingangle output in the related art. Thus, the firing angle value determinedin the previous operation of the internal combustion engine in operatingrange II is output as the new starting value for range II on leavingthis range II. Then in operating range IIa, the firing angle is restoredto the mapped firing angle with this restoration being accomplished withincrements using a smaller step height and step width.

At time t2 the internal combustion engine again changes ranges.Specifically, operation of the internal combustion engine changes fromoperating range IIa to operating range Ib, where b denotes that this isthe second occurrence of this operating range in FIG. 3. In the processaccording to the present invention, a check is performed at time t2 todetermine whether load dynamics also occur when the change in rangesoccurs. If load dynamics occur in changing ranges, the firing anglesaved for this operating range in a previous operation of the internalcombustion engine (not shown here) is output as the starting value foroperation in this operating range. Then this firing angle is againrestored to the mapped firing angle or until knocking occurs.

At time t3 there is another change of ranges, where operation of theinternal combustion engine changes from operating range Ib to operatingrange IIb. At time t3, a check is again performed to determine whetherload dynamics ΔL occur. No load dynamics are detected at time t3, so thecurrent firing angle on leaving operating range Ib is retained as thestarting value for operating range IIb. This prevents sudden changes infiring angle with a change in operating range of the internal combustionengine.

Ultimately, the respective firing angle before knocking occurs in thevarious operating ranges can be determined and entered in the currentengine characteristics map for determining the firing angle in such away that the previous value entered there is overwritten. Thus thefiring angle map is constantly being updated and the firing angle outputis optimized for the operation of the internal combustion engine. Thus,this is a type of self-learning firing angle map that comes closer andcloser to the knock limit. There are various possibilities for selectingor defining a firing angle that replaces the mapped firing angle savedin the memory. Thus, for example, the mapped firing angle storedpreviously can be overwritten by the last firing angle before knockingoccurs as the new firing angle for this operating point or the firstfiring angle after knocking occurs. It is also conceivable to apply aslight correction, such as a definable firing angle displacement ZW, tothe firing angle before knocking occurs and to enter this value in theengine characteristics map. Moreover, it is also possible for thiscorrection to the mapped firing angle to be made only when the mappedfiring angle saved in the memory differs from the new firing angle to beentered in the engine characteristics map by a predetermined differenceDZW.

FIG. 4 shows a schematic diagram of the process according to the presentinvention. First, the load L and the speed N are determined in step 9,whereupon a query 10 determines whether there has been a change inranges. If this is the case, a subsequent query 11 determines whetherload and/or speed dynamics are occurring at the same time. If the answerto this question 11 is "yes," the firing angle saved for this operatingrange in an adaptive engine characteristics map is output as thestarting firing angle in step 12 or, if the answer is "no," the firingangle of the operating range recently left is retained in step 13. Ifinquiry 10 concerning whether there has been a change of ranges isanswered as "no," the knock control process continues in the known way,i.e., query 14 determines whether knocking K has occurred. If this isthe case, knock control is performed by retarding the firing angle by apredetermined amount ΔZW in step 15, and the current retardation issaved in an adaptive characteristics map. If no knocking is found inquery 14, query 16 determines whether the current firing angle changeΔZW and the stored firing angle differ by a predetermined thresholdvalue DZW. If this is the case, the answer "yes" to this question leadsto step 15, where the current firing angle change is stored in theadaptive engine characteristics map. However, if query 16 is answered inthe negative, the current change in firing angle is set to zero and themapped firing angle is output for controlling the operation of theinternal combustion engine.

There are various possibilities for learning the knock limit. Forexample, the firing angle immediately before knocking K occurs or thefiring angle immediately after knocking K occurs, i.e., after the firstcorrection to retard the angle, can be entered in the enginecharacteristics map. However, it is also conceivable to shift the firingangle before knocking occurs by a predetermined value for the change infiring angle and to save this value in the engine characteristics mapfor the purpose of learning the knock limit.

What is claim is:
 1. A process for adaptive knock control of an internalcombustion engine having a plurality of operating ranges defined byoperating parameters of the engine, the method comprising the stepsof:when a knocking occurs in a cylinder of the engine during operationof the engine in one of the operating ranges of the engine, retarding afiring angle for the cylinder; when no cylinder knocking occurs,restoring the firing angle by advancing the firing angle; saving theretarded firing angle corresponding to the one of the operating rangesof the engine in an adaptive characteristics map, the adaptivecharacteristics map containing the plurality of operating ranges, theretarded firing angle being saved when the engine leaves the one of theoperating ranges; and outputting the saved retarded firing angle fromthe adaptive characteristics map when the engine returns to the one ofthe operating ranges and, simultaneously, at least one of load dynamicsand speed dynamics occurs.
 2. The process according to claim 1, furthercomprising the step of retaining a preceding retarded firing angle whenthe engine changes operating ranges and the at least one of the loaddynamics and the speed dynamics is less than a predetermined value. 3.The process according to claim 1, further comprising the step ofentering the firing angle before the knocking occurs into thecharacteristics map.
 4. The process according to claim 1, furthercomprising the step of entering the firing angle after the knockingoccurs into the characteristics map.
 5. The process according to claim1, further comprising the steps of:applying a firing angle correction tothe firing angle before the knocking occurs; and entering the correctedfiring angle into the characteristics map.
 6. The process according toclaim 1, further comprising the step of replacing the saved retardedfiring angle in the characteristics map with a new retarded firing angleonly when a difference between the saved retarded firing angle and thenew retarded firing angle is greater than a preselected threshold value.